In the field of data and computer communications there is an increasing need for high speed/high bandwidth products. Prior art references relating to packet switching and more specifically to data stream decoding and pertinent to the present invention include:                U.S. Pat. No. 5,509,006,        JP 6/276198,        EP 767565,        EP 953897,        U.S. Pat. No. 5,594,869The problem of extracting address information in a switch from a packet in a data stream is in the prior art solved by applying masks on the content of one or more delay lines to filter out the required information. One disadvantage with this approach is the difficulty to adjust the switch to new communication protocols, because the masks are hardware implemented. Another disadvantage with the prior art is that the data in the delay line is only accessible at a certain position or certain positions, instead of being available all the time they reside in the delay line.        
Accordingly, it is an object of the present invention to provide a device for improved programmable datastream analysis in the context of packet switching. In the context of this document a datastream can be any type of data stream, e.g. a bytewise Ethernet datastream in a computer network, including an Ethernet packet with different combinations of contents.